Initial test build. Looks like everything works

Dockerfile

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+# The first stage just builds up the modpack
+FROM alpine:latest AS build
+
+# Args
+ARG MINECRAFT_VERSION="1.16.5"
+ARG FORGE_VERSION="36.1.4"
+
+# The actual setup work
+COPY start-server.sh /minecraft/start-server.sh
+WORKDIR /minecraft
+RUN apk add curl openjdk8-jre &&\
+	curl -L "https://files.minecraftforge.net/maven/net/minecraftforge/forge/${MINECRAFT_VERSION}-${FORGE_VERSION}/forge-${MINECRAFT_VERSION}-${FORGE_VERSION}-installer.jar" -o installer.jar &&\
+	java -jar installer.jar --installServer &&\
+	echo "eula=true" > eula.txt &&\
+	rm installer.jar installer.jar.log && \
+	ln -s "forge-${MINECRAFT_VERSION}-${FORGE_VERSION}.jar" server.jar
+
+# The second stage is the actual container
+FROM openjdk:8
+WORKDIR /minecraft
+COPY --from=build /minecraft .
+CMD [ "bash", "start-server.sh" ]
+EXPOSE 25565